Pumps of both the fixed and free type often include a control valve means axially positioned above an engine and a production pump means, and it is not unusual for the engine chambers to be positioned at each extremity of the pump means, as evidenced by my previously issued U.S. Pat. No. 3,650,640. However, in this particular fixed-type pump, provisions must be made within the side wall of the pump housing for various fluid flow paths, as for example, from the valve means to the engine means, and consequently, the diameter of the pistons thereof are reduced a corresponding amount.
Some oil wells are extremely deep and small in diameter and require a slim pump for accommodation within the slim borehole. Some of these wells are high volume producers and require a high volume pump. Accordingly, the present invention provides an improvement over U.S. Pat. No. 3,650,640 by the provision of a free-type pump which eliminates the heretofore necessary internal flow passageways formed within the side wall of the pump and engine housing. This improvement is brought about by a novel combination of flow passageways formed externally of the pump housing and other passageways formed within the reciprocating centrally located control rod of the pump assembly.